Several people have been arrested in connection with the Pakistan mosque bombing that killed over 100 people on Monday, Peshawar police told Reuters on Wednesday.
"We have found some excellent clues, and based on these clues we have made some major arrests," Peshawar Police Chief Ijaz Khan told Reuters.
"We can't rule out internal assistance but since the investigation is still in progress, I will not be able to share more details."
The bomber struck on Monday as hundreds of worshippers gathered for noon prayers in a mosque that was built specifically for the police and their families living in a highly fortified area.
Investigators, who include counter-terrorism and intelligence officials, are focusing on how the attacker managed to breach the military and police checkpoints leading into the Police Lines district that is home to middle- and lower-ranking police personnel and their families.
Defence Minister Khawaja Asif had said the bomber was in the first row in the prayer hall when he struck. Remains of the attacker had been recovered, provincial Police Chief Moazzam Jah Ansari told Reuters.
"We believe the attackers are not an organised group," he added.
The most active militant group in the area, the Pakistani Taliban, also called Tehreek-e-Taliban Pakistan (TTP), has denied responsibility for the attack, which no group has claimed so far.
Interior Minister Rana Sanaullah had told parliament a breakaway faction of the TTP was to blame.
The blast demolished the upper storey of the mosque.
Peshawar sits on the edge of the Pashtun tribal lands, a region mired in violence for the past two decades.